Since you say you're co-authoring, it's especially important that you precisely define who owns what, whether individually or jointly, and mark the relevant materials accordingly. Otherwise, some day you may find yourself handicapped in the use of your own work, no matter how good your friendship with your partner may be.
Trademarks are used to prevent pirating of your good name and your product's identity, but they don't actually protect the product.
Patents are fairly involved and expensive, and supposedly, in order to be granted a patent you have to demonstrate that you have a new and non-obvious idea and that there is no prior art that expressed that idea or made the idea an obvious conclusion. Of course in the USA and quite a few other countries that whole concept is pretty much a joke right now, but things are quite likely to change in the not-too-distant future.
Nolo Press provides some excellent books on protecting IP for software developers, though if you're really serious, it's a good idea to consult a legal professional specializing in IP.
Customer surveys are for companies who didn't pay proper attention to begin with.